1. Field of the Invention
The present invention relates to an output apparatus such as a printer connected to a host computer through a bidirectional interface, and a method therefor.
2. Related Background Art
A printer always requires certain consumable materials. For example an ink jet printer requires ink sealed in an ink cartridge. Also an output apparatus for forming an image on a sheet by the electrophotographic technology utilizes toner for color development. In the following description, such consumable materials, including ink, will be exemplified by toner. As the toner is consumed in the printing operation, it has to be replenished by the user. For facilitating such toner replenishing operation, the toner packaged in a cartridge is widely employed in recent printing apparatus. When the toner in the cartridge is used up, the user removes the empty toner cartridge from the printing apparatus and replaces it with a new toner cartridge.
As the printing operation can naturally be no longer executed when the toner is used up, a warning mechanism is often employed to provide the user with a prior warning before the toner is completely exhausted. For example a mechanical sensor, provided in the toner cartridge, detects a low remaining amount of the toner and displays a warning on the liquid crystal display of the printing apparatus or sends a status signal to the host computer, thereby giving the user a warning through the monitor of the host computer.
Recognizing such prior warning, the user can take various measures such as preparing or purchasing a toner cartridge, avoiding the output operation for a large job, or increasing the density of the output image.
Also in case the printing apparatus -has to discriminate the toner cartridges of different kinds, the shape of such cartridge is made partly different according to the kinds and such difference is detected by a mechanical sensor provided in the printing apparatus.
However, such conventional method of mechanically detecting the remaining toner amount is capable of detecting that the remaining toner amount has reached a certain level, but is associated with a drawback that the remaining amount thereafter or the running-out time of the toner cannot be known at all.